The present invention relates to a new and improved method for inspecting O-rings and more specifically to a method of determining the diameter, thickness and/or locating flaws in the surface of an O-ring.
Standard elastomeric O-rings are frequently used as cheap seals in non-critical areas subjected to relatively mild operating conditions. When standard elastomeric O-rings have been used as seals in critical areas subjected to severe operating conditions, problems have been encountered. For the most part, these problems are a result of the fact that O-rings are commonly manufactured at high production rates with a minimum of care in order to minimize the cost of the O-rings. As a result, in critical use areas, O-rings must be 100% inspected.
Inspection of O-rings is a labor-intensive, time-consuming and tedious process which is presently performed manually without the use of sophisticated gauges or automated equipment. Each O-ring is inspected to be certain that its inside diameter, outside diameter, and/or thickness is within specified tolerance ranges. The determination of the inside and/or outside diameter of an O-ring is difficult since the O-ring is readily deflected and tends to distort whenever it is engaged by a solid measuring device. When the O-ring is held in an upright orientation by engaging one radial segment of the O-ring, the O-ring tends to distort under the influence of its own weight.
In addition, O-rings are also inspected for numerous types of surface flaws. These surface flaws include backrind, blister, excessive trimming, flash, flow marks, foreign materials, mismatch, mold deposit indentations, non-fill, off-register, parting line indentation, parting line projection, and porosity.
Backrind is a longitudinal recess of a wide angle U-like or W-like cross section located at a mold section parting line. It is caused by thermal expansion over a sharp mold edge or by premature cure. Blisters are voids or holes in the body of the O-ring. Flash is a very thin gage, sometimes film-like, material which extends from parting line projections. Flow marks are recesses caused by incomplete flow of the material forming the O-ring. Foreign materials are any extraneous, embedded matter or depression formed in the surface of the O-ring.
In regard to the other surface defects, mismatch occurs when the cross sectional radius in one ring half is unequal to that of the other ring half. This is caused by a dimensional difference in mold halves. Mold deposit indentations are caused by a build up of hardened deposits adhering to the mold cavity and result in indentations, and rough surface texture of the O-ring. Non-fill results in randomly spaced, irregularly shaped, surface indentations having a course texture. Off-register is misaligned O-ring halves caused by a lateral shift of one mold cavity plate relative to another mold cavity plate. Parting line indentation is a shallow, saucer-like recess located on a parting line and caused by a deformity in the mold edge. Parting line projection is a continuous ridge of material situated on the parting line and caused by worn or excessively rounded mold edges. Finally, porosity is the presence of numerous minute voids or sponginess in the O-ring.
The inspecting of O-rings is difficult and time consuming due to the fact that if the O-rings are to be used in critical situations to provide a desired sealing action, the O-rings must be accurately shaped to the desired dimensions and be free of surface flaws. Thus, an O-ring for critical use may typically have an inside or outside diameter which can vary by as little as 0.005 inches and a thickness which can vary by as little as 0.003 inches. When the obtaining of the desired sealing action requires precision dimensioning of an O-ring, the O-ring must be free of all but the very smallest surface flaws. Thus, a surface imperfection having a width of 0.002 inches can, in some situations, lead to a seal failure.